The present invention relates to steering arms for railway trucks. More specifically, the junction of the side arms and cross-beam in a U-Shaped steering arm is provided with a compound fillet to improve the flexural strength and reduce the sensed stress loads between the side arm and cross-beam without encumbering or interfering with either the wheel position or operation.
Side trucks or steering arms for a vehicle truck are utilized to control railroad car trucks, especially against hunting or lateral movement during radial travel around curves. An early truck model with steering arms is illustrated in U.S. Pat. No. 2,360,061 to L. B. Jones, which provided a car truck with two interconnected sub-components capable of independent swiveling movement. The steering arms project diagonally from a common central point to projecting side arms coupled to the axles of each wheelset, and the car trucks independently swivel relative to the car body while rounding track curves. The diagonal braces emanating from the center pivot are illustrated with generally single radiused corners at their intersection with the side arms, which radius is usually large. In these early-model trucks, the large radii steering arms are not limited by potential interference with ancillary truck components, such as bolsters, side frames and wheels.
The objective of any of the radial trucks is adjustment of the axles, bolster and side frame motion to accommodate radial movement around curves for relief of the lading from the shocks and jars incident to the contact between rails and wheel flanges. In U.S. Pat. No. 2,296,106 to Holland et al, a pair of yokes is attached to the saddle of the car at each side of the car, and each yoke is operatively connected to the center of the bolster. The yoke arms extend from the bolster center at a generally acute angle to the longitudinal direction of car travel with the sidearms formed to couple with saddles at each wheel. The separation distance between bolster, side frame and wheels in this assembly provides adequate clearance for the yoke and yoke operation.
Recent developments in steering arms for articulated railway trucks have concentrated on problems of lateral restraint and yaw flexibility between the two wheelsets of a truck, to prevent high speed hunting. These changes in steering arm structures for self-steering wheelsets are illustrated in U.S. Pat. No. 4,781,124 to List. However, it is evident in the illustrations that the sidearms of the steering arm structures project generally normal to the steering arm cross-beam in proximity to the wheel, which minimizes the available space for the components.
The lack of a large clearance distance for the steering-arm components is readily apparent in the List--'124 patent and, as a consequence, the intersection of the steering-arm cross-beam and sidearm is approximately a right angle. In operation, there is a repeated flexural load paced upon the joint intersection of these modern steering arm structures. As the noted clearances between the wheel and steering arm are minimal, it has been necessary to utilize a circular radius in the intersecting shoulder, which is adequate for structural arrangements, but would preferably be stronger to reduce the stresses on the sidearm, such as by enlarging the circular radius. However, the wheel, side frame and bolster clearances and steering arm size have combined to preclude or limit development of a stronger junction relationship between the side arms and cross-beam.
Although it is known that the addition of a greater mass to a joint or a larger radius in a corner junction would act to increase the strength of the junction, these alternatives are not available in many modern steering arm apparatus with the above-noted clearance constraints. A discussion of alternatives for increasing strength of intersecting arms or segments is provided in Stress Concentration Factors, by R. E. Peterson, John Wiley and Sons, 1974. The effects of fillets with a noncircular component and their impact on the stress concentration are discussed at page 83-86, ibid. It is noted that although circular fillets are utilized for ease of machining and drafting, they do not provide the minimum stress concentration.
The development of stronger steering-arm component junctions or connections would allow tighter control of both the lateral restraint and yaw flexibility of the wheelsets, the truck and thus the rail car with minimal, if any, added cost. Further, greater control of truck "hunting," especially in curves and at high speeds, enhances the safe operation of railway cars.